How to judge sign-up or login at Post-Login Action?

I’ve setup Stripe customer and Auth0 user connection according to following example:
And I’ve implemented our website with auth0-nextjs.

Firstly it looks good at both Google and database connection (username/password), but there is an issue with the one of the database connection user.
He continues failed to login because the logins_count is still 1 after signup and logout. I’ve expected the logins_count will increase to 2 at the second login attempt, but it remained to 1. Then the Post Login Action denied his login as he has been already registered at Stripe by existing customer ID at app_metadata.

I found Auth0 FAQ says that there is a case logins_count will not increment. When the above user attemped to login, the auth0 universal login page didn’t shown. So this could be the case.

I think we can safely return; without denying access at the check of data integrity described in the article: Auth0 Developer Resources

This will be a workaround for this case (maybe unsafe). But the root problem is that there is no actual way to judge sign-up or login at Login Action.
Is there a best practice for detecting sign-up or login at Post-Login custom Action?